Ferritic stainless steel

ABSTRACT

A ferritic-type stainless steel suitable for manufacture into sheet and strip form that can be used for production operations involving stamping, punching, piercing, blanking and drawing by high-speed press production.

United States Patent Inventor Wesley Kulltu New Kennlngtnn, Pa.

Appl. No. 802,632

Filed Feb. 26, 1969 Patented Sept. 21, 1971 Assignee Allegheny Ludlum Steel Corporation Pittsburgh, Pa.

FERRlTlC STAINLESS STEEL 5 Claims, N0 Drawings U.S. Cl 75/124, 75/ 126 H Int. Cl ..C22c 37/10, C220 39/02 Field of Search ..75/126, 126 D, 124, 126 H [56] References Cited UNITED STATES PATENTS 2,736,649 2/1956 Phillips 75/126 D 3,250,611 5/1956 Lula 75/126 D 3,347,663 10/1967 Bicber 75/128 3,455,681 7/1969 Moskowitz 75/126 Primary Examiner-Hyland Bizot Attorneys-Richard A. Specr and Vincent G. Gioia ABSTRACT: A ferritic-type stainless steel suitable for manufacture into sheet and strip form that can be used for production operations involving stamping, punching, piercing, blanking and drawing by high-speed press production.

FERRlTlC STAINLESS STEEL A number of existing ferritic stainless steels, while possessing adequate corrosion resistance in mildly corrosive media, suffer from relatively poor fabricationcharacteristics due to surface and subsurface titanium stringers. Typical of these alloys which contain titanium are AlSl Type 409, Type 499, and the commercial stainless steel known as MF-1 produced and developed by Allegheny Ludlum Steel Corporation. The titanium stringers which may occur in these alloys are a source of breakage during forming and may be responsible for excessive die wear due to their abrasiveness. Moreover, in certain applications, such as automotive thermostats, windshield wipers, beverage tubing, etc., that are subject to moderately severe corrosive conditions, the foregoing grades may be unsatisfactory.

The present invention provides a ferritic stainless steel of relatively low cost and adequate corrosion resistance for even relatively severe corrosive conditions but which is relatively free of harmful titanium stringers and particles. Alloys in accordance with the invention are particularly useful in manufacturing low-cost welded tubing from strip and sheet and for replacement of brass, copper, aluminum and carbon steel fabricated articles in applications where relatively substantial corrosion resistance is required and where fabrication includes processing by high-speed punching presses which typically involve stamping, punching, piercing, blanking and drawing. Illustrative of the potential uses of alloys in accordance with the invention are in the manufacture of shot gun cases and automotive water pump seals. An additional advantage of steels in accordance with the invention is their ability to be bright annealed and produce pickled finishes with good solid surface capable of withstanding the aforementioned fabricating operations. Compositions of the invention possess tensile properties as follows:

Tensile 65-75,0()0 p.s.i. Yield 3545,000 p.s.i. Elongation 23-35 Rockwell 13" 70-75 ln accordance with the invention there is provided a ferritic stainless steel consisting essentially of about up to 0.06 percent carbon, 0.2 to 1.0 percent manganese, preferably 0.3 to 0.5 percent manganese, 0.2 to 1 percent silicon, preferably 0.3 to 0.5 percent silicon, 14.5 to 15.5 percent chromium, preferably 14.7 to 15.3 percent chromium, 0.15 to 0.3 percent aluminum, 0.01 to 0.1 percent titanium, preferably 0.05 to 0.1 percent titanium, and the balance essentially iron with usual steel making residuals. The carbon content is limited because additional amounts beyond about 0.06 percent may result in a steel which is somewhat difficult to weld due to formation of more martensite. The upper limits of the alloying constituents, e.g. manganese and chromium, are restricted to avoid developing unnecessary hardness and strength which would interfere unduly with formability, however, a chromium content of 14.5 to 15.5 percent is necessary to assure the degree of corrosion resistance required for the applications to which the present invention is particularly well suited. Such applications typically involve a degree of corrosion resistance sufficient to withstand moderately severe corrosive conditions such as would be present in automotive components exposed to salt spray contact. The manganese and aluminum contents must be controlled to facilitate hot rolling. The aluminum limits of 0.15 to 0.3 percent are established to provide adequate weldability which is reduced if less than about 0.15 percent aluminum is included and to assure adequate ducti bility and formability which may be reduced if too much aluminum, e.g. more than 0.3 percent aluminum, is present. Titanium is included in amounts of at least 0.01 percent to improve formability, however, amounts of titanium of greater than 0.1 percent are avoided to minimize stringer formation which, as mentioned previously, has an undesirable effect on stamping die wear.

As an illustration of the practice of the invention. three hot rolled coils of the composition described in table 1 were produced. One coil 36 igches X 0.08 inches was box annealed, wheelabrated and pickled. Two coils 26 inches X 0.08 inches were box annealed, wheelabrated, pickled and edge trimmed.

Table 1 below summarizes the transverse mechanical properties of the material produced in the cold rolled condition. in addition, micrographic analysis of the material in the fully annealed state confirmed the absence of large titanium stringer-type inclusions which would be detrimental to die wear.

TABLE I (Strip) Nominal check Broad range chemistry analysis Carbon Up to 0.06. 0.05 max 0. 045 Manganese .e 0.2 to 1.0 0.30/0.50 0.42 Phosphorus 0.025 max. 0. 020 Sulfur 0.025 max 0.011 Silicon. 0.2 to 1 0.30/0.50 0. 32 Chromium. 14.5 to 15.5 14.7/15.3. 15. 04 Nickel 0 30 max. 0. 22 Aluminum 0.15 to0.3 0.23 Titanium 0.01 to 0.1- 0.05/0.10 O. 095

TRANSVERSE MECHANICAL PROPE RTIES Mechanical properties of cold rolled material after fur- Typlcal nace annealing at mechanical 1700 F. for five (5) properties minutes Yield, p.s.i Gil/75,000 38,000

Tensile, p.s.i is/45,000 67, 000

Elongation in 2", percent. 25/35 32 Rockwell B 70/75 1 "30T 64 l Converted B 71.

While several embodiments of my invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the appended claims.

lclaim:

1. A ferritic stainless steel consisting essentially of about up to 0.06 percent carbon, 0.2 to 1.0 percent manganese, 0.2 to 1 percent silicon, 14.5 to 15.5 percent chromium, 0.15 to 0.3 percent aluminum, 0.01 to 0.1 percent titanium, and the balance essentially iron with usual steelmaking residuals.

2. A ferritic stainless steel according to claim 1 having 14.7 to 15.3 percent chromium.

3. A fcrritic stainless steel according to claim 1 having 0.3 to 0.5 percent silicon.

4. A ferritie stainless steel according to claim 1 having 0.05 to 0.1 percent titanium.

5. A ferritic stainless steel according to claim 1 having 0.3 to 0.5 percent manganese. 

2. A ferritic stainless steel according to claim 1 having 14.7 to 15.3 percent chromium.
 3. A ferritic stainless steel according to claim 1 having 0.3 to 0.5 percent silicon.
 4. A ferritic stainless steel according to claim 1 having 0.05 to 0.1 percent titanium.
 5. A ferritic stainless steel according to claim 1 having 0.3 to 0.5 percent manganese. 